Sports posts

ABSTRACT

The present invention relates to sports post for athletics, which are light, tough, easily to set up or taken down. The sports post have two or more fiber reinforced plastic hollow tubes that are fitted and connected together. A screw-type extension and retraction mechanism is built within the posts. The sports posts have a rod shaped member fixed to one hollow tube that passes through the through-hole of an element fixed to another hollow tube. Another embodiment of the present invention includes sports posts in which the reinforcing fiber layer from which the hollow tubes are composed include, a laminate structure of sheet-shaped material. The sports posts include a laminate structure of a sheet shaped material in which the fiber is carbon fiber and filaments thereof are unidirectionally arranged, and of a filament bundle structure layer which can be seen from outside.

This application is the national phase under 35 U.S.C. §371 of prior PCTInternational Application No., PCT/JP96/02899 which has an Internationalfiling date of Oct. 04, 1996 which designated the United States ofAmerica, the entire contents of which are hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to sports posts such as net posts, goalposts and posts for athletics, which are light, tough, easily set up andtaken down and, moreover, excellent aesthetically.

TECHNICAL BACKGROUND

Hitherto, the net posts used in volleyball and tennis, and the sportsposts for soccer, rugby, American football and athletics, etc, have beenmade of iron or stainless steel metal. In the case of net posts inparticular, in order to counter the bending moment generated whentension is applied to the net wire, the main structural parts have beenmade of fairly thick-walled metal from the point of view of strength.Further, the general extension/retraction mechanism in such posts isusually a system in which two or more hollow tubes are connected byfitting together telescopically, with the inner tube(s) being raised orlowered by means of a screw mechanism. With this extension/retractionmechanism, when an operating handle is introduced into an insertion holeprovided in the outer tube side face and a built-in bolt rotated via abevel gear, the inner tube to which a nut is fixed is raised and, inthis way, adjustment is possible to the appropriate net height for eachsporting event. When rotating the bolt, it is necessary to preventco-rotation of the nut portion. In conventional steel posts, a lead-ingroove is cut in the surface of the inner tube to which the nut isfixed, running in the axial direction of the tube. A key provided in theouter tube engages this lead-in groove. In this way, it is possible toraise and lower the inner tube without co-rotation occurring along withthe rotation of the bolt.

Conventional thick-walled metal sports posts are extremely heavy, andconsiderable physical effort is required in their setting up and takingdown. For example, taking the case of net posts, which are one type ofsports posts, when these are employed in a multi-purpose location suchas a gymnasium, unlike in a dedicated court, the posts have to befrequently set up and taken down, and where the net posts are long and,consequently, heavy, like the posts for volleyball, their setting up andtaking down is accompanied by physical strain on the part of the user.

DISCLOSURE OF THE INVENTION

The sports posts relating to the present invention are sports postscharacterized in that two or more fibre reinforced plastic hollow tubesare fitted and connected together and, moreover, a screw type extensionand retraction mechanism is built-in and, preferably, they are sportsposts where a rod shaped member fixed to one hollow tube passes throughthe through-hole of an element fixed to another hollow tube.

Further, another embodiment of the present invention includes sportsposts where the reinforcing fibre layer from which the hollow tubes arecomposed has a laminate structure of a sheet-shaped material of thefibre, preferably predominantly sheet-shaped material in which the fibreis carbon fibre and filaments thereof are unidirectionally arranged.More preferably, these sports posts include a laminate structure of afilament bundle structure layer which can be seen from the outside. Asthe filament bundle structure, woven materials or a wound filamentbundle, etc, are used.

The present invention is characterized in that the main structural partsof the sports posts are composed of a fibre reinforced plastic which islight and tough, and while still maintaining the strength to withstand alarge bending moment, a considerable reduction in weight is achieved.With this invention, it is possible to markedly reduce the physicalstrain at the time of the setting up and taking down of sports postswhere frequent such setting up and taking down is required, inparticular with net posts for volleyball and tennis.

Further, in the case where two or more fibre reinforced plastic hollowtubes are fitted and connected together, and then extended or retracted,if a key lead-in groove for preventing co-rotation is provided bycutting the tube surface, like in the case of conventional steel posts,the reinforcing fibre of the fibre reinforced plastic is severed andthere is a substantial reduction in strength. In the present invention,by employing a special co-rotation prevention mechanism in which a rodshaped member is fixed to one hollow tube and passes through thethrough-hole of an element fixed to another hollow tube, there isobtained an expansion/retraction mechanism in which there is no severingof the reinforcing fibre and no impairment of the inherent strength ofthe tube, and unnecessary cost increases are avoided.

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a side view of an extending/retracting net post forvolleyball, which is one sports post of the present invention.

FIG. 2 is a sectional view of the raising/lowering mechanism within thesports post of the present invention.

FIG. 3 is a side view showing an L-shaped bar which is one example ofthe rod-shaped member used for preventing co-rotation.

FIG. 4 is the cross-section through A--A in FIG. 2.

FIG. 5 is the cross-section through B--B in FIG. 2.

FIG. 6 is a partially enlarged view showing one example of the surfaceof a sports post of the present invention, and illustrates the decoratedstate when the outermost layer portion is composed of a wovenfabric-form filament bundle structure layer.

EXPLANATION OF THE NUMERICAL CODES

1: outer tube

2: inner tube

3: handle insertion hole

4: raising/lowering handle

5: bevel gear

6: raising/lowering screw bolt

7: raising/lowering screw nut

8: rod shaped member

9: raising/lowering screw bolt fixture

10: lead-in hole

Optimum Configurations for Practising the Invention

As the fibre reinforced plastic referred to in the present invention,there can be employed any kind of fibre reinforced plastic where resinand fibre are combined to achieve a reduction in weight and where thefibre provides the strength but, in terms of the objectives of thepresent invention, one that provides both lightness and high strength isrequired. As the reinforcing fibre for realising this objective, a hightenacity fibre of tensile strength desirably at least 20 g/d isdesirable. Further, from the need to keep the post deflection to samelevel as iron or stainless steel, a high tenacity fibre with a hightensile modulus is used. As a high tenacity fibre which meets thisobjective, there is preferably used fibre of tensile elastic modulus atleast 5,000 kgf/mm2 and, more preferably, at least 20,000 kgf/mm2.Further, in the case where two or more hollow tubes are fitted andconnected together, it is especially preferred that on the outer tubeside where bending stresses are concentrated there be used high tenacityfibre of still higher elastic modulus, for example carbon fibre thetensile elastic modulus of which is raised to the 30,000 kgf/mm2 levelby a graphitization treatment (graphitized fibre), or the like.

Such fibre is produced according to the factors of material, spinningmethod and after-processing. In regard to the fibre material factor,there can be used aromatic polyamide fibres, carbon fibres, glass fibresand light metal fibres, etc. As fibre spinning method factors, there canbe used fibre spun using a high molecular weight polymer as the startingmaterial, after which drawing is carried out at a high draw ratio, andas fibre after-processing factors there can be used fibre drawn whileexposing to radiation including a plasma discharge. As fibre based onthe latter two methods there can be used polyester fibre, polyamidefibre, polyolefin fibre, polyvinyl alcohol fibre and polyacrylonitrilefibre, etc. Of these fibres, for the purposes of the present invention,from the point of view of the thermal properties when moulding as acomposite material there is preferably used a fibre which, along withbeing of high tenacity and high modulus, also has excellent heatresistance. In this sense, carbon fibre (including graphitized fibre) isespecially preferred.

The chief objective of such fibre is the reinforcement of the post and,consequently, it is preferably combined with the resin in a form andstructure such that the properties of the said fibre are fullymanifested. In regard to said fibre form or structure, it is preferredthat the post be produced using a sheet-shaped material comprising saidfibre, that is to say at least one type comprising paralleled fibresheet, woven material or nonwoven material, wound to produce a hollowshape. Specifically, there is desirably employed a sheet-wound structureproduced by, for example, firstly forming a filament bundle of saidfibre into a paralleled fibre sheet-shaped material or into a wovenmaterial, and then winding this. Further, it is also possible to form ahollow wound structure by winding a plurality of layers of the filamentbundle directly onto a core without said filament bundle being made insheet form, which is referred to as a filament-wound structure, and suchstructures are also desirably employed. Of course, the fibre reinforcedlayer may also be constructed by using the two types of structuretogether.

In regard to such sheet-shaped materials or filament bundles, in orderto increase the strength of the posts utilising the tenacity of hightenacity fibre, for at least one of the components in said posts thereis preferably employed a structure having a parallel unidirectionalarrangement in the circumferential direction of said post, specificallythe structure applied to a fishing rod. Again, said sheet-shapedmaterial or filament bundle is desirably given a discharge treatment ora matrix resin affinity treatment with the objective of improving theadhesion to the resin.

Furthermore, where the reinforcing fibre layer of the outermost layer isa filament bundle structure layer which can be seen from the outside anda transparent resin is used as the matrix resin, it is possible to usethe pattern of the filament bundle structure layer as a decoration as itis, so its design characteristics are excellent. Here, a filament bundlestructure is a woven material or filament bundle wound structure and,furthermore, in order that such a structure be visible from the outside,the width of the filament bundle viewed planarly is at least 1 mm and,more preferably, at least 2 mm. Moreover, as specific woven materialstructures, plain weave, twill weave and satin weave are the basicstructures, and these and derivative weaves based thereon may beappropriately used according to the decoration required. For example, inthe case of a twill weave the structure is somewhat larger so thepattern is larger, while with a satin weave, since it is possible toreduce weave crossover points compared to plain and twill weaves, it ispossible to produce a pattern which is extremely smooth and lustrous.

From the point of view of realising a reduction in weight, the matrixemployed in the fibre reinforced composite material is preferably one oflow specific gravity and, for this reason, the use of a resin ispreferred. As said resin, there may be used a natural resin, but the useof a high molecular weight synthetic resin is desirable. Of suchsynthetic resins, the use of a thermosetting resin with outstandingthermal and mechanical properties is preferred. Amongst thermo-settingresins, phenolic resins, epoxy resins or unsaturated polyester resinsare desirably employed in terms of toughness and processingcharacteristics.

As described above, if the hollow tubes from which the sports posts areconstructed are moulded by means of a fibre reinforced compositematerial, there is a considerable improvement in particular in terms oflightness when compared to conventional metal-made posts. Furthermore,in terms of bending strength and bending rigidity, the performanceconferred is the same as metal-made posts. However, in regard to themode of failure when an excessive load is applied to the post, there isa strong possibility of differences arising between a metal and a fibrereinforced material. That is to say, the relation between the load anddeflection exhibits essentially elastic characteristics up to failure inthe case of a fibre reinforced composite material, whereas in the caseof a metal, while elastic characteristics are shown up to a certainload, once the yield point has been exceeded the rigidity then fallsgreatly and plastic deformation characteristics are shown. In otherwords, even though the load countering capacity of both is at the samelevel, in the metal case a ductile failure mode is displayed whereaswith the fibre reinforced material a brittle failure mode is shown.Consequently, at the practical level, in the case where an unexpectedlygreat load is applied to the post, with a metal tube sufficient warningis obtained up to failure occurring, so, in this respect, metal issuperior to a fibre reinforced material.

Hence, from the point of view of compensating for the disadvantages ofboth, the production of the hollow tubes from which the sports posts arecomposed in the form of a hybrid structure of fibre reinforced plasticand metal is more preferred than constructing the post from a fibrereinforced plastic alone. Here, in the hybrid structure, it will sufficethat the fibre reinforced material and the metal are closely affixed inlayered fashion, and the lamination pattern is not especiallyrestricted. However, from a processing standpoint, a structure in whichthe metal layer is closely affixed at the hollow tube inner layer sideis preferred. That is to say, generally speaking, in the formation of ahollow tube by means of a fibre reinforced composite material, there isconducted the winding of a sheet-shaped material or filament bundle ofsaid fibre as explained above and, in such circumstances, the winding isperformed using a metal rod known as a mandrel as the core. If a hollowtube made of metal is used instead of this mandrel then, as well as itbeing possible to dispense with the normally required stage ofwithdrawing the mandrel, it is also possible to obtain the desiredhybrid structure. The material for this metal-made hollow tube is notparticularly restricted but, for the purposes of reducing the weight,the selection of a metal of low specific gravity such as aluminium ispreferred. Again, the wall thickness needs to be decided based on abalance between the weight reducing effect and the brittle failureprevention effect, and this will vary according to the diameter of thehollow tube and the type of metal used. However, a lower limit of wallthickness is required sufficient to withstand the pressure of thetriple-roll or the rolling table, etc, in the reinforcing fibresheet-shaped material winding stage.

Next, in the present invention, two or more fibre reinforced plastichollow tubes are fitted and connected together, and when providing theextension/retraction function a novel screw-type extension/retractionmechanism is employed. In short, in the provision of a built-inextension/retraction mechanism with a co-rotation preventing function,not only from the point of view that a cutting process such as providinga lead-in groove by cutting the inner tube as in the case ofconventional steel posts leads to a substantial reduction in thestrength, but also from the point of view of the resulting inevitablecost increase, this kind of means has not been employed, and insteadthere has been employed a special co-rotation prevention mechanismutilising a rod shaped member.

The extension/retraction mechanism of the present invention is nowexplained based on the drawings. The extension/retraction mechanism ofthe present invention is a system whereby, to a nut portion provided onone inner tube, there is fitted the bolt of a bolt rotation mechanismprovided on the inside of another outer tube, and by rotating the boltof this bolt rotation mechanism via a bevel gear, the said inner tube israised or lowered, but the characteristic feature lies in the fact thatco-rotation is prevented by passing a rod shaped member fixed to thesaid one hollow tube through a through-hole fixed in the other hollowtube.

FIG. 1 is a view of the entire structure of a net post for volleyball towhich the present invention has been applied, and FIG. 2 is across-sectional view showing the raising/lowering mechanism in theinterior. Below, the extension and retraction mechanism of the net postin this present patent application is explained using these drawings.Reference numeral 1 is an outer tube and reference numeral 2 is an innertube, and these are fitted and connected together in the manner of atelescope or aerial. The post height is adjusted by raising or loweringthe inner tube. In the case where the net post is to be extended orretracted, a bolt rotation mechanism is used in which, firstly, thehandle 4 used for raising/lowering is inserted into the handle insertionhole 3 provided in the outer tube side face and the rotation thereof istransmitted to a bevel gear 5. By means of this bevel gear, as well asthe axis of rotation being made to change direction so that it matchesthe tube axis, the rotation is transmitted to raising/lowering screwbolt 6 which is internally fixed in the outer tube. In the inner tube,there is fixed raising/lowering screw nut 7 which corresponds to theraising/lowering screw bolt 6, and inner tube 2 is raised or loweredaccording to the rotation of the screw bolt 6. Thus far, the mechanismis the same as a conventional built-in screw type extension andretraction mechanism.

A characteristic feature of the present invention lies in the mechanismfor preventing the co-rotation of the raising/lowering screw nut 7. Thatis to say, internal screw-based extension/retraction is only possible bysuppressing rotation of the screw nut, but naturally this suppression ofrotation must not inhibit the raising/lowering movement of the innertube. Accordingly, in a conventional steel-made net post, a lead-ingroove is cut into the surface of the inner tube 2, running in the tubeaxial direction, and a key which has been provided in the outer tube 1fits into this lead-in groove, so that by the movement of this keywithin the lead-in groove co-rotation is prevented without obstructingthe extension/ retraction.

In the present invention, the co-rotation of the raising/lowering screwnut is prevented by a completely different method from this conventionalmechanism. That is to say, there is employed a mechanism whereby a rodshaped member fixed to one hollow tube passes through the through holeof an element fixed to another hollow tube. Explaining a specificexample by means of FIG. 2, rod shaped member 8 is fixed toraising/lowering nut 7 such that it is parallel to but does not touchraising/lowering screw bolt 6 and, furthermore, this rod shaped member 8passes through lead-in hole 10 provided in raising/lowering screw boltfixture 9 which is fixed within the outer tube 1. Here, FIG. 3 shows anexample of the rod shaped member (an L-shaped bar) used in the presentinvention. Furthermore, FIG. 4 is a sectional view through A--A in FIG.2, and it shows the L-shaped bar in FIG. 3 bolted to raising/loweringscrew nut 7. FIG. 5 is a sectional view through B--B in FIG. 2 and showsthe L-shaped bar suspended from raising/lowering screw nut 7 passingthrough the lead-in hole 10 provided in raising/ lowering screw boltfixture 9.

By making the length of the rod shaped member at least longer than theactual extension/retraction length, this rod shaped member 8 passesfreely up and down through lead-in hole 10, merely preventingco-rotation of the screw nut. The rod shaped member may be of any shapesuch as a circular or angular column, but it is necessary that it bestraight and without differences in level, grooves or projections, etc,which would inhibit movement in its lengthwise direction. The materialof the rod shaped member is not particularly restricted providing it hasa strength and stiffness such that breakdown or large distortions do notoccur when preventing the co-rotation.

The improvement effect in terms of the strength properties of a net postbased on the structure according to the present invention will differconsiderably depending on the tube material. Thus, when the tubematerial used is a fibre reinforced plastic for the purposes of weightreduction, then the improvement effect in this respect is veryconsiderable compared to a steel product. In the case where a lead-ingroove is provided in the same way as a steel post, cutting is carriedout at a width of about 5 mm and to a depth of about 3 mm from the tubesurface, but since the bending strength and rigidity of the tube aremanifested based on the tensile strength and tensile rigidity of thereinforcing fibre in the fibre reinforced plastic, following the cuttingthe reinforcing fibres in the fibre reinforced composite material layerare severed in proportion to the depth of the groove and the strengthproperties are not at all as desired. Since, the wall thickness of theinner hollow tube can be reduced the higher the tenacity of thereinforcing fibre, cutting a groove in the conventional manner leads toa fatal reduction in the strength. Thus, where a net post is moulded bymeans of a fibre reinforced composite material, the constructionemployed in the present invention in which no cutting is required isessential.

The sports posts of the present invention can also be used for exampleas posts for supporting nets such as those for golf practice ranges andbaseball grounds, etc, where it is important that they be strong andlight, and where they also have the considerable feature that setting upand taking down is easy. The sports posts referred to in the presentinvention include net posts for volleyball, tennis, badminton, golf,baseball and table tennis, goal posts for soccer, rugby, Americanfootball, handball and hockey, and also the various kinds of posts andframeworks such as hurdles used in athletics, etc. If the sports postsof the present invention are employed as the various kinds of posts forball games in multi-purpose locations like gymnasia where the setting upand taking down of said posts is frequently carried out, then theeffects in terms of reducing the physical effort at the time of suchsetting up and taking down of the posts are markedly apparent. As statedabove, the net posts for sports in the present invention can be employedwidely for games and sports conducted both indoors and outdoors, andinclude rod shapes and frameworks. Further, providing the tubes arehollow, the cross-sectional shape of such tubes does not have to becircular and can be changed to be elliptical, angular, etc, according tothe usage objectives, and it is possible to construct various types ofapparatus employed in said games and sports.

EXAMPLES Example 1

The extending/retracting net post shown in FIG. 1 was constructed as anet post for volleyball. Firstly, the hollow tubes forming the mainstructural members of the net post comprised fibre reinforced plastic inwhich carbon fibre filament was the reinforcing fibre. As the carbonfibre filament, there was selected a high modulus type of strength 40g/d and tensile modulus 30,000 kgf/mm², and sheet prepreg in which epoxyresin was the matrix was moulded in the form of tubes of wall thickness6.0 mm by a sheet winding method. As the actual sheet winding method,the rolling table method was selected and, as the laminate pattern,unidirectional prepreg was oriented at 0° and ±45° to thecircumferential direction and a strengthwise balance obtained.

In relation to this net post, the number of plies in each direction wasdetermined such that the 0° and ±45° balance ratio was set at 4:1.Further, for decoration in the outermost layer, a 5-end satin weavesheet was employed. These sheet prepregs were firstly laid-up bywrapping around a mandrel while applying a pressure of 3 kg/cm² with arolling table and then wrapping tape wound around, after which curingwas carried out at 130° C. in a curing oven and, finally, the mandrelwithdrawn. Two hollow tubes of different tube diameter obtained by thismoulding method were fitted together in telescopic fashion, then theparts other than the main structural members fitted, namely the pulleyportion, wire take-up portion and the screw bolt and nut for raising andlowering, etc, and the volleyball net post thus assembled. Now, in thenet post of this example a steel L-shaped bar as shown in FIG. 3 wasalso fixed to the raising/lowering screw nut 7 shown in FIG. 2, and thisbar was made to pass through lead-in hole 10 provided in theraising/lowering screw bolt fixture 9. Again, the length of the L-shapedbar was set to be sufficient such that even when the net post wasextended to its maximum it did not come out of the lead-in hole. Now,because the fibre layer was visible through the transparent epoxy resin,the net post surface obtained was decorated as shown in FIG. 6 by meansof the woven texture of the outermost layer.

Comparative Example 1

In this comparative example, a net post was constructed having a screwtype raising and lowering mechanism of the same kind as in conventionalsteel posts. Thus, firstly, hollow tubes of wall thickness 6.0 mm inwhich the reinforcing fibre was carbon fibre filament were an identicalmethod to that in Example 1, but the outer face of the inner tube wascut to form a groove of depth 3.0 mm and width 5.0 mm continuously inthe lengthwise direction. A key to fit this groove was provided at theinner wall portion of the outer tube tip, and then the net postassembled with this key fitted into the groove in the outer wall of theinner tube.

Comparative Example 2

This was a conventional steel-made commercial net post for volleyballand, in the same way as in Comparative Example 1, a groove was cut inthe outer face of the inner tube and a key provided on the inner wall atthe tip of the outer tube. The wall thickness of the tubes was 5.2 mm.

Example 2

Hollow tubes were moulded by the sheet winding method using carbon fibrefilament as the reinforcing fibre in the same way as in Example 1, butinstead of the mandrel an aluminium tube of wall thickness 1.0 mm wasused as the core, and a laminate structure of aluminium and a carbonfibre reinforced resin layer obtained. The adhered state of thealuminium and the fibre reinforced resin layer was sufficient forpractical purposes, and there was no particular need to use a primer orthe like. Further, the total wall thickness of the hollow tube obtainedwas made 6.0 mm, the same as in Example 1, and the internal raising andlowering mechanism was also the same.

Table 1 shows the results of an evaluation of the operation of theraising and lowering device in these net posts and of the bendingcharacteristics of the hollow tubes. The operation of the raising andlowering device was judged based on the resistance when turning theraising and lowering handle by hand without introducing wire tension. Inregard to the bending characteristics, reference was made to theRecognised Standards Confirmation Method relating to safety and qualityof volleyball equipment as stipulated by the Product Safety Committee.Firstly, in a state such that the post height was held at 2430 mm, aninitial tension of 50 kgf was introduced and the net extended andstabilised for at least one minute. Next, taking this state as thestandard, a further 200 kgf load was applied and after stabilizing byholding for at least one minute, the level of post deflection wasmeasured by means of a scale. According to the Recognised Standard ofthe Product Safety Committee, when a load of 250 kgf is applied to asteel-made post, the deflection must be no more than 130 mm.

As explained above, the volleyball net posts based on the presentinvention were made of carbon fibre reinforced plastic and so, whencontrasted with Comparative Example 2 which was a conventionalsteel-made net post, the weight was less than 1/3, and not just thecarrying of the posts at the time of setting up and taking down but alsothe operation of the raising and lowering device was light and easy.Again, in the case of Comparative Example 1, which was made of the samecarbon fibre reinforced plastic and only the raising/lowering mechanismwas the same as in a conventional steel post, while there was nodifference in the ease of operation, the level of deflection of the postwhen the tension was applied was greater than that in Example 1 andComparative Example 2 when tension was applied. In order to avoid anydanger, measurement was halted at the point when the deflection exceeded200 mm. Thus, as well as exhibiting a deflection which would leave theplayers feeling uneasy, the strength of the post in Comparative Example1 where the inner tube had been subject to cutting was also clearlyreduced, and it was confirmed that the post was impossible to usewithout markedly increasing the wall thickness. In Example 2, while theweight and deflection were slightly increased, the operationalcharacteristics of the raising/lowering device were no different whencompared to Example 1 and, in practical terms, the difference in weightand deflection were such as to be hardly noticed. From the above resultsit is clear that, in the case where a fibre reinforced plastic is usedas the main structural material of the net posts, by means of theconstruction in this present application in which no cutting is carriedout it is possible for the first time to realise satisfactory lightness,raising/lowering operational properties and bending characteristics(level of deflection).

                                      TABLE 1                                     __________________________________________________________________________                       Comparative                                                                          Comparative                                                      Example 1                                                                           Example 1                                                                            Example 2                                                                            Example 2                                    __________________________________________________________________________    Tube diameter (external                                                                    76.3 mm                                                                             76.3 mm                                                                              76.3 mm                                                                              76.3 mm                                      diameter of outer tube)                                                       Tube wall thickness                                                                        6.0 cm                                                                              6.0 cm 5.2 cm 6.0 cm                                       Weight (per set)                                                                           20.8 kg                                                                             20.7 kg                                                                              71.4 kg                                                                              22.4 kg                                      Raising/lowering operational                                                               ⊚                                                                    ⊚                                                                     ∘                                                                        ⊚                             characteristics                                                               Level of defection (tension                                                                118.4 mm                                                                            above  115.8 mm                                                                             128.2 mm                                     250 kgf)           200 mm                                                     __________________________________________________________________________     Note:                                                                         The weight includes the pulley portion, wire takeup portion and the screw     bolt/nut for raising lowering, etc.                                      

We claim:
 1. A post system for a sports net comprising:a first hollowtube; a second hollow tube, said first hollow tube being disposed withinsaid second hollow tube; a screw nut fixing element being disposedwithin said first hollow tube; a screw fixing element being disposedwithin said second hollow tube; a screw being rotatably supported bysaid screw fixing element and being operatively connected to said screwnut fixing element; a screw drive mechanism disposed within said secondhollow tube and operatively connected to said screw; and a rodpreventing rotation of said screw nut fixing element, said rod beingslidably engaged with one of said screw fixing element and said screwnut fixing element and being fixed to one of said screw fixing elementand said screw nut fixing element, said first hollow tube and saidsecond hollow tube including a fiber reinforced plastic.
 2. The postsystem for a sports net of claim 1, wherein said reinforced plasticcomprises carbon fibers.
 3. The post system for a sports net of claims 1or 2, wherein said fiber reinforced plastic comprises a laminate ofreinforcing fiber sheets.
 4. The post system for a sports net of claim3, wherein said fiber reinforced plastic sheets comprise at least one ofunidirectionally arranged filament sheets, woven materials, andnon-woven materials.
 5. The post system for a sports net of claim 3,wherein said fiber reinforced plastic comprises unidirectionallyarranged filament sheets and a filament bundle structure layer disposedon an external surface of said reinforced plastic material.
 6. The postsystem for a sports net of claim 5, wherein said filament bundlestructure layer comprises woven material.
 7. The post system for asports net of claim 5, wherein said filament bundle structure layercomprises a wound layer.
 8. The post system for a sports net of claim 5,wherein said filament bundle structure has a width of at least 1 mm. 9.The post system for a sports net of claim 8, wherein said filamentstructure has a width of at least 2 mm.
 10. The post system for a sportsnet of claim 1, wherein said fiber reinforced plastic comprises filamentbundle wound layers.
 11. The post system for a sports net of claims 1 or2, wherein reinforcing fibers of said fiber reinforced plastic have astrength of at least 20 g/d.
 12. The post system for a sports net ofclaims 1 or 2, wherein reinforcing fibers of said fiber reinforcedplastic have a tensile modulus of at least 5,000 kgf/mm².
 13. The postsystem for a sports net of claims 1 or 2, wherein reinforcing fibers ofsaid fiber reinforced plastic have a tensile modulus of at least 20,000kgf/mm².
 14. The post system for a sports net of claims 1 or 2, whereinsaid fiber reinforced plastic includes at least one of polyester fiber,polyamide fiber, polyolefin fiber, polyvinyl alcohol fiber,polyacrylonitrile fiber, light metal fiber, and glass fiber.
 15. Thepost system for a sports net of claims 1 or 2, wherein said first hollowtube has reinforced fibers of a first modulus, said second hollow tubehas reinforced fibers of a second modulus, said second modulus is higherthan said first modulus.
 16. The post system for a sports net of claims1 or 2, wherein said fiber reinforced plastic includes a metal layer,said metal layer being an innermost layer of said fiber reinforcedplastic.
 17. The post system for a sports net of claims 1, 3 or 10,wherein said fiber reinforced plastic includes a matrix resin, saidmatrix resin is disposed on an external surface and is a transparentthermosetting resin.